With an increasing interest in sustainable energy production there is a focus on using photovoltaic modules for producing electric power. Photovoltaic (PV) modules include a plurality of photovoltaic (PV) cells, that are also known as solar cells. Usually several solar modules are connected in series to form a string of modules. A DC output voltage provided by the string may then be converted into an AC voltage, such as, for example, a voltage suitable to be supplied to a power grid or to drive a motor.
In an ideal case each of the modules connected in series provides the same output voltage. In real photovoltaic arrangements there may be modules that provide a lower voltage than other modules. This may be due to wear, corrosion of contacts within the module, and the like.
In order to optimize the output of a solar arrangement with a plurality of PV modules a Maximum Power Point (MPP) tracker may be coupled to each of the modules. The MPP trackers monitor the output powers of the individual modules and operate the individual modules in their MPP. Through the MPP trackers the output powers of the individual modules are known so that a deviation of the output power of one module from the output power of other modules may easily be detected, so that suitable measures can be taken.
MPP trackers, however, are expensive so that in large solar power plants a MPP tracker is at most coupled to one string with a plurality of modules but not to the individual modules.
Nevertheless, there is a need to monitor in a cost efficient way the output voltage of power sources, such as PV modules, in a string with a plurality of power sources connected in series.